1. Field of the Invention
The present invention relates to an image capturing apparatus and a control method thereof.
2. Description of the Related Art
Heretofore, digital still cameras and digital video cameras using an image sensor such as a CCD image sensor or a CMOS image sensor have been widely used. However, the dynamic range (latitude) of these image sensors is narrow compared with silver halide film. For this reason, when capturing a high contrast scene, loss of tone detail in low luminance portions (plugged-up shadows) and loss of tone detail in high luminance portions (blown-out highlights) tend to occur.
Systems capable of controlling the dynamic range automatically have been proposed in response to such problems.
For example, in Japanese Patent Laid-Open No. 2005-209012, it is proposed, in the case where it is detected from a captured image that the main subject is backlit or in a high contrast scene, to specify a black saturation point and a white saturation point from a histogram of the image, and perform tone correction such that the brightness of the main subject is correct.
Also, in Japanese Patent Laid-Open No. 2004-186876, it is proposed to acquire two types of images with different dynamic ranges using an image sensor disposed with high sensitivity light receiving elements and low sensitivity light receiving elements, by capturing the same scene with the light receiving elements having different sensitivities, and combine these captured images according to a scene analysis result.
There is also a digital camera (Canon EOS 5D Mark II) that has a shooting mode (highlight tone priority mode) for shifting the sensitivity setting range one step higher and suppressing blown-out highlights in high luminance portions.
However, with the method of Japanese Patent Laid-Open No. 2005-209012, an effect of widening the dynamic range is not obtained, since the points at which the sensor becomes saturated do not change, despite there being an effect of increasing contrast to the eye.
Also, with the method of Japanese Patent Laid-Open No. 2004-186876, an effect of widening the dynamic range is obtained, but there is the problem of the cost involved, since a special image sensor disposed with light receiving elements having different sensitivities needs to be used.
Also, with the digital camera having the tone priority mode, to obtain an image capture result in which blown-out highlights in high luminance portions are suppressed, the user needs to explicitly set the tone priority mode before performing image capture. Also, depending on the scene, there may be cases where the effect of the tone priority mode is not really noticeable or where it would be better to prioritize other conditions rather than suppressing blown-out highlights in high luminance portions when performing image capture. For example, in the case where the subject is a landscape, desirably there are no blown-out highlights in high luminance portions, but in the case where the subject is a person, desirably the brightness of the person's face is correct, even if the background is slightly blown out. In other words, to obtain an appropriate image capture result by making use of the tone priority mode, the user is required to be able to discriminate scenes appropriately, in addition to setting the tone priority mode.